Plasmodium falciparum Prp16 homologue and its role in splicing

Large numbers of Plasmodium genes have been predicted to have introns. However, little information exists on the splicing mechanisms in this organism. Here, we describe the DExD/DExH-box containing Pre-mRNA processing proteins (Prps), PfPrp2p, PfPrp5p, PfPrp16p, PfPrp22p, PfPrp28p, PfPrp43p and PfBrr2p, present in the Plasmodium falciparum genome and characterized the role of one of these factors, PfPrp16p. It is a member of DEAH-box protein family with nine collinear sequence motifs, a characteristic of helicase proteins. Experiments with the recombinantly expressed and purified PfPrp16 helicase domain revealed binding to RNA, hydrolysis of ATP as well as catalytic helicase activities. Expression of helicase domain with the C-terminal helicase-associated domain (HA2) reduced these activities considerably, indicating that the helicase-associated domain may regulate the PfPrp16 function. Localization studies with the PfPrp16 GFP transgenic lines suggested a role of its N-terminal domain (1-80 amino acids) in nuclear targeting. Immunodepletion of PfPrp16p, from nuclear extracts of parasite cultures, blocked the second catalytic step of an in vitro constituted splicing reaction suggesting a role for PfPrp16p in splicing catalysis. Further we show by complementation assay in yeast that a chimeric yeast-Plasmodium Prp16 protein, not the full length PfPrp16, can rescue the yeast prp16 temperature-sensitive mutant. These results suggest that although the role of Prp16p in catalytic step II is highly conserved among Plasmodium, human and yeast, subtle differences exist with regards to its associated factors or its assembly with spliceosomes.